Huge sunspot group — Active region 9393 as seen by MDI hosted the largest sunspot group observed so far during the current solar cycle. On 30 March 2001, the sunspot area within the group spanned an area more than 13 times the entire surface of the Earth! It was the source of numerous flares and coronal mass ejections, including the largest flare recorded in 25 years on 2 April 2001. Caused by intense magnetic fields emerging from the interior, a sunspot appears to be dark only when contrasted against the rest of the solar surface, because it is slightly cooler than the unmarked regions.
Courtesy of SOHO/MDI consortium. SOHO is a project of international cooperation between ESA and NASA.